This invention relates to a novel load switching control circuit for controlling the switching of new lamp banks of illumination control systems employing dimming control, and more specifically relates to a novel control system which ensures successful switching of new lamp banks into the system without producing annoying effects on those working in areas which are illuminated by dimmed lamps which are energized from the same control system.
It is well known that a large number of banks of gas discharge lamps, such as fluorescent lamps, can be energized from a common power source and controlled in illumination output by a common dimmer control circuit. In such systems, however, if a new lamp bank is to be added to the existing energized banks, some means must be provided to apply a sufficiently high voltage to the new bank to ensure its adequate striking.
U.S. Pat. No. 4,350,935, issued Sept. 21, 1982, entitled Gas Discharge Lamp Control, in the name of Joel S. Spira et al, and assigned to the assignee of the present invention describes circuits for applying additional energy to new banks of lamps which are to be connected in parallel with other banks of lamps which are already excited but are driven at a relatively lower voltage in order to dim their illumination output. The additional energy was taken from various energy storage means and required fairly complicated additional circuitry for its implementation.
Other systems are known in which, when additional banks are to be added to previously dimmed banks of lamps, the entire circuit is switched to full output voltage, thus causing the dimmed lamps to immediately increase from their dimmed illumination level to their full level but assuring adequate striking of the new lamps. However, the flicker which is caused by immediately changing light intensity from the dimmed value to the full value will be annoying to occupants of the area in which the illumination had been dimmed. After a short time, for example, 90 seconds, the lamps are returned to the dimmed setting.